Its called 'Operation #SignDavesCas, it is how you can enter a contest to sign Dave's cast.

Last week, when Dave Grohl was performing at a FooFIghters show in Sweden, he broke his leg, forcing the band to cancel the rest of their European tour.  He's on his way to recovery, but fans are invited to send him well-wishes.  A couple of ways to go about this you can log into 'SignDavesCast' or just tweet a message to Dave with the hashtag #signDavescast and you could be one of 300 tweets to go on a cast gifted to Dave later this summer.
The tweets will appear on a cast on the website, with about 300 of the best tweets will be chosen to be printed on a flexible cast sleeve and that will be presented to Dave while he recuperates from his post-injury surgery.

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